Enhanced combined tumor-specific oncolysis and suicide gene therapy for prostate cancer using M6 promoter

Enzyme pro-drug suicide gene therapy has been hindered by inefficient viral delivery and gene transduction. To further explore the potential of this approach, we have developed AdIU1, a prostate-restricted replicative adenovirus (PRRA) armed with the herpes simplex virus thymidine kinase (HSV-TK). In our previous Ad-OC-TK/ACV phase I clinical trial, we demonstrated safety and proof of principle with a tissue-specific promoter-based TK/pro-drug therapy using a replication-defective adenovirus for the treatment of prostate cancer metastases. In this study, we aimed to inhibit the growth of androgen-independent (AI), PSA/PSMA-positive prostate cancer cells by AdIU1. In vitro the viability of an AI- PSA/PSMA-expressing prostate cancer cell line, CWR22rv, was significantly inhibited by treatment with AdIU1 plus GCV (10 microg ml(-1)), compared with AdIU1 treatment alone and also cytotoxicity was observed following treatment with AdIU1 plus GCV only in PSA/PSMA-positive CWR22rv and C4-2 cells, but not in the PSA/PSMA-negative cell line, DU-145. In vivo assessment of AdIU1 plus GCV treatment revealed a stronger therapeutic effect against CWR22rv tumors in nude mice than treatment with AdIU1 alone, AdE4PSESE1a alone or in combination with GCV. Our results demonstrate the therapeutic potential of specific-oncolysis and suicide gene therapy for AI-PSA/PSMA-positive prostate cancer gene therapy.     

Gene therapy for prostate cancer by controlling adenovirus E1a and E4 gene expression with PSES enhancer

PSES is a chimeric enhancer containing enhancer elements from prostate-specific antigen (PSA) and prostate-specific membrane antigen (PSMA) genes that are prevalently expressed in androgen-independent prostate cancers. PSES shows strong activity equivalent to cytomegalovirus (CMV) promoter, specifically in PSA/PSMA-positive prostate cancer cells, the major cell types in prostate cancer in the absence of androgen. We developed a recombinant adenovirus (AdE4PSESE1a) by placing adenoviral E1a and E4 genes under the control of the bidirectional enhancer PSES and enhanced green fluorescent protein gene for the purpose of intratumoral virus tracking under the control of CMV promoter. Because of PSES being very weak in nonprostatic cells, including HEK293 and HER911 that are frequently used to produce recombinant adenovirus, AdE4PSESE1a can only be produced in the HER911E4 cell line which expresses both E1 and E4 genes. AdE4PSESE1a showed similar viral replication and tumor cell killing activities to wild-type adenovirus in PSA/PSMA-positive prostate cancer cells. The viral replication and tumor cell killing activities were dramatically attenuated in PSA/PSMA-negative cells. To test whether AdE4PSESE1a could be used to target prostate tumors in vivo, CWR22rv s.c. tumors were induced in nude mice and treated with AdE4PSESE1a via intratumoral and tail vein injection. Compared to tumors treated with control virus, the growth of CWR22rv tumors was dramatically inhibited by AdE4PSESE1a via tail vein injection or intratumoral injection. These data show that adenoviral replication can be tightly controlled in a novel fashion by controlling adenoviral E1a and E4 genes simultaneously with a single enhancer.     

Tissue prostate-specific antigen facilitates refractory prostate tumor progression via enhancing ARA70-regulated androgen receptor transactivation

Despite being well recognized as the best biomarker for prostate cancer, pathophysiologic roles of prostate-specific antigen (PSA) remain unclear. We report here that tissue PSA may be involved in the hormone-refractory prostate cancer progression. Histologic analyses show that the increased tissue PSA levels are correlated with lower cell apoptosis index and higher cell proliferation rate in hormone-refractory tumor specimens. By stably transfecting PSA cDNA into various prostate cancer cell lines, we found that PSA could promote the growth of androgen receptor (AR)-positive CWR22rv1 and high-passage LNCaP (hormone-refractory prostate cancer cells) but not that of AR-negative PC-3 and DU145 cells. Surprisingly, the protease activity of PSA is not crucial for PSA to stimulate growth and promote AR transactivation. We further showed that increased PSA could enhance ARA70-induced AR transactivation via modulating the p53 pathway that results in the decreased apoptosis and increased cell proliferation in prostate cancer cells. Knockdown of PSA in LNCaP and CWR22rv1 cells causes cell apoptosis and cell growth arrest at the G(1) phase. In vitro colony formation assay and in vivo xenografted tumor results showed the suppression of prostate cancer growth via targeting PSA expression. Collectively, our findings suggest that, in addition to being a biomarker, PSA may also become a new potential therapeutic target for prostate cancer. PSA small interfering RNA or smaller molecules that can degrade PSA protein may be developed as alternative approaches to treat the prostate cancer.     

Response of prostate cancer to anti-Her-2/neu antibody in androgen-dependent and -independent human xenograft models.

Antibody to the Her-2/neu gene product has been shown to inhibit the growth of breast cancer cells overexpressing Her-2/neu and to have clinical utility in treating breast cancer. We studied a recombinant, humanized anti-Her-2/neu antibody (Herceptin) in preclinical models of human prostate cancer. The androgen-dependent CWR22 and LNCaP human prostate cancer xenograft models and androgen-independent sublines of CWR22 were used. Her-2/neu staining of the parental, androgen-dependent, and androgen-independent CWR22 tumors and LNCaP tumors demonstrated variable Her-2/neu expression. Herceptin was administered i.p. at a dose of 20 mg/kg twice weekly after the xenograft had been established. No effect of Herceptin on tumor growth was observed in any of the androgen-independent tumors; however, significant growth inhibition was observed in both of the androgen-dependent xenograft models, CWR22 (68% growth inhibition at the completion of the experiment; P = 0.03 for trajectories of the average tumor volume of the groups) and LNCaP (89% growth inhibition; P = 0.002). There was a significant increase in prostate-specific antigen (PSA) index (ng PSA/ml serum/mm3 tumor) in Herceptin-treated androgen-dependent groups compared with control (CWR22, 18-fold relative to pretreatment value versus 1.0-fold, P = 0.0001; LNCaP, 2.35-fold relative to pretreatment value versus 0.6-fold, P = 0.001). When paclitaxel (6.25 mg/kg s.c., five times/week) was given to animals with androgen-dependent and -independent tumors, there was growth inhibition in each group. Paclitaxel and Herceptin cotreatment led to greater growth inhibition than was seen for the agents individually. Thus, in these prostate cancer model systems, Herceptin alone has clinical activity only in the androgen-dependent tumor and has at least an additive effect on growth, in combination with paclitaxel, in both androgen-dependent and androgen-independent tumors. Response to Herceptin did not correlate with the PSA levels, because the PSA index markedly increased in the Herceptin-treated group, whereas it remained constant in the control group. These results suggest the utility of Herceptin in the treatment of human prostate cancer.     

FTY720, a fungus metabolite, inhibits in vivo growth of androgen-independent prostate cancer

FTY720, a derivative of fungus, has demonstrated dramatic anticancer effect in several malignancies recently. Our study evaluates the therapeutic potential of FTY720 in the treatment of androgen-independent prostate cancer using a human prostate cancer xenograft in nude mice. CWR22R, an androgen-independent human prostate tumor xenograft was inoculated into castrated nude mice and the animals were administrated with either normal saline or FTY720 (10 mg/kg) through intraperitoneal (i.p.) injection for 20 days. Body weight and tumor volume were recorded every 2 days, and serum prostate specific antigen (PSA) levels were also measured before and after the treatment. The effect of FTY720 on tumor cell proliferation was examined using antibodies against PCNA and Ki-67 by immunohistochemical staining, MTT assay and colony forming assay, whereas apoptotic effect of FTY720 was evaluated by TUNEL assay and immunostaining using antibodies against cleaved caspase 3 and Bcl-2. In addition, the potential inhibitory effect of FTY720 on prostate cancer angiogenesis and metastasis was investigated by immunostaining of CD31, VEGF, E-cadherin and beta-catenin. Our results showed that FTY720 treatment led to suppression of CWR22R tumor growth without causing any detectable side effects in nude mice. The FTY720-induced tumor suppression was correlated with decreased serum PSA level as well as reduced proliferation rate, suppression of angiogenic factors, and restoration of E-cadherin and beta-catenin expression. In addition, the FTY720-treated tumors showed increased apoptosis rate demonstrated by increased TUNEL- and cleaved caspase 3-positive cells, and decreased Bcl-2 expression. Our results suggest a potential novel agent in the suppression of androgen-independent prostate cancer.     

Suberoylanilide hydroxamic acid, an inhibitor of histone deacetylase, suppresses the growth of prostate cancer cells in vitro and in vivo

Suberoylanilide hydroxamic acid (SAHA) is the prototype of a family of hybrid polar compounds that induce growth arrest in transformed cells and show promise for the treatment of cancer. SAHA induces differentiation and/or apoptosis in certain transformed cells in culture and is a potent inhibitor of histone deacetylases. In this study, we examined the effects of SAHA on the growth of human prostate cancer cells in culture and on the growth of the CWR22 human prostate xenograft in nude mice. SAHA suppressed the growth of the LNCaP, PC-3, and TSU-Pr1 cell lines at micromolar concentrations (2.5-7.5 microM). SAHA induced dose-dependent cell death in the LNCaP cells. In mice with transplanted CWR222 human prostate tumors, SAHA (25, 50, and 100 mg/kg/day) caused significant suppression of tumor growth compared with mice receiving vehicle alone; treatment with 50 mg/kg/day resulted in a 97% reduction in the mean final tumor volume compared with controls. At this dose, there was no detectable toxicity as evaluated by weight gain and necropsy examination. Increased accumulation of acetylated core histones was detected in the CWR22 tumors within 6 h of SAHA administration. SAHA induced prostate-specific antigen mRNA expression in CWR22 prostate cancer cells, resulting in higher levels of serum prostate-specific antigen than predicted from tumor volume alone. The results suggest that hydroxamic acid-based hybrid polar compounds inhibit prostate cancer cell growth and may be useful, relatively nontoxic agents for the treatment of prostate carcinoma.     

Comparative RNA-seq analysis reveals potential mechanisms mediating the conversion to androgen independence in an LNCaP progression cell model

The androgen-independent phenotype is an important symptom of refractory prostate cancer. However, the molecular mechanisms underlying this phenotypic conversion remain unclear. Using RNA-seq analysis of androgen-dependent prostate cancer cells (LNCaP) vs. androgen-independent cancer cells (LNCaP-AI-F), we identified 788 differentially expressed genes, 315 alternative splicing events, and eight novel LNCaP-AI-F-specific fusion genes. The fusion genes EIF2AK1-ATR and GLYR1-SLC9A8 were predicted to be damaging and oncogenic. We also observed dramatic changes in androgen receptor (AR)-mediated pathway molecules, including prostate-specific antigen (PSA, a major biomarker of prostate cancer) and AR variants, as well as neuroendocrine-like (NE-like) and tumor stem cell-like characteristics, during androgen-independent phenotype progression. Our findings provide new insights into the regulatory complexities of refractory prostate cancers.     

Antiproliferative effects of AVN944, a novel inosine 5-monophosphate dehydrogenase inhibitor, in prostate cancer cells

Inosine 5-monophosphate dehydrogenase II, a key enzyme in the de novo synthesis of purine nucleotides, is expressed in prostate tumors and prostate cancer cells. AVN944 is a new, specific, noncompetitive IMPDH inhibitor. In this study, we investigated the effects of IMPDH inhibitor AVN944 on LNCaP, CWR22Rv1, DU145 and PC-3 human prostate cancer cells. AVN944 inhibited proliferation of these 4 prostate cancer cell lines and was associated with cell cycle G1 arrest of LNCaP cells and S-phase block of androgen-independent CWR22Rv1, DU145 and PC-3 cells. AVN944 induced caspase-dependentand caspase-independent cell death in LNCaP, CWR22Rv1, and DU145 cells. AVN944 induced expression of p53-target proteins Bok, Bax and Noxa in androgen-responsive cell lines and suppressed expression of survivin in prostate cancer cells regardless of their androgen sensitivity. AVN944 also induced differentiation of androgen-independent prostate cancer cells as indicated by morphological changes and increased expression of genes coding for prostasomal proteins, keratins and other proteins, including tumor suppressor genes MIG-6 and NDRG1. AVN944-differentiated androgen-independent DU145 and PC-3 cells are sensitized to TRAIL-induced apoptosis as demonstrated by induction of caspases and PARP cleavage. In summary, AVN944 inhibited the growth of human prostate cancer cells by inducing cell cycle arrest, cell death as well as differentiation. AVN944 is a novel, promising therapeutic agent that might be combined with other agents for treatment of human prostate cancer.     

Androgen withdrawal inhibits tumor growth and is associated with decrease in angiogenesis and VEGF expression in androgen-independent CWR22Rv1 human prostate cancer model

Recent evidence suggests that androgens stimulate growth of human prostate cancer partly by regulating expression of growth factors such as vascular endothelial growth factor (VEGF) in vitro and in vivo. In this study, we used CWR22Rv1, a novel androgen-responsive but androgen-independent human prostate cancer model, to evaluate the effect of androgen withdrawal on tumor growth, expression of VEGF and the cell proliferation marker Ki-67, and angiogenesis. A time-release testosterone pellet was implanted three days before inoculation of CWR22Rv1 cells in the mice. The tumor volumes were measured every three days. Serum PSA was measured on days 1, 12, 20, 27 and 34 post inoculation. Castration was performed on the 20th day post inoculation. Immunohistochemical assays were used to evaluate cell proliferation and microvessel density. Enzyme-linked immunosorbent assay (ELISA) was used to quantify VEGF expression. The average tumor volumes in the castration group on the 27th and 34th days were 122 and 168 mm3, respectively, compared to 156 and 210 mm3 in the non-castration group (p<0.01). Serum PSA level in the castration group decreased to about 41% of the level of the non-castration group (p<0.01). The VEGF protein levels in the tumors of castrated and non-castrated mice on day 34 were 0.62 pg and 1.36 pg/100 microg total protein, respectively (p<0.001). The mean percentage of Ki-67-positive tumor cells in the castrated and non-castrated groups were 1.8% and 2.8%, respectively (p=0.015). The mean microvessel densities in the castrated and non-castrated groups were 15 and 22 vessels/field, respectively (p<0.01) We conclude androgen withdrawal reduced both VEGF and microvessel density, and this was associated with decreased cellular proliferation in androgen-independent CWR22Rv1 human prostate cancer tumor in vivo.     

Honokiol, a natural plant product, inhibits the bone metastatic growth of human prostate cancer cells

BACKGROUND: Honokiol, a soluble nontoxic natural product derived from Magnolia spp., has been shown to induce apoptosis in malignant cells. The effect of honokiol and the combined therapy with docetaxel on prostate cancer (PCa) growth and bone metastasis was investigated in experimental models. METHODS: The in vitro proapoptotic effects of honokiol on human androgen-dependent and -independent PCa, bone marrow, bone marrow-derived endothelial, and prostate stroma cells were investigated. Honokiol-induced activation of caspases was evaluated by Western blot and FACS analysis. To confirm the cytotoxicity of honokiol, mice bone was inoculated in vivo with androgen-independent PCa, C4-2 cells and the effects of honokiol and/or docetaxel on PCa growth in bone were evaluated. Daily honokiol (100 mg/kg) and/or weekly docetaxel (5 mg/kg) were injected intraperitoneally for 6 weeks. PCa growth in mouse bone was evaluated by radiography, serum prostate-specific antigen (PSA) and tissue immunohistochemistry. RESULTS: Honokiol induced apoptosis in all cell lines tested. In PCa cells honokiol induced apoptosis via the activation of caspases 3, 8, and 9 and the cleavage of poly-adenosine diphosphate ribose polymerase in a dose- and time-dependent manner. Honokiol was shown to inhibit the growth and depress serum PSA in mice harboring C4-2 xenografts in the skeleton and the combination with docetaxel showed additive effects that inhibited further growth without evidence of systemic toxicity. Immunohistochemical staining confirmed honokiol exhibited growth-inhibitory, apoptotic, and antiangiogenic effects on PCa xenografts. CONCLUSIONS: The combination of honokiol and low-dose docetaxel may be used to improve patient outcome in androgen-independent prostate cancer with bone metastasis.     

Lovastatin enhances adenovirus-mediated TRAIL induced apoptosis by depleting cholesterol of lipid rafts and affecting CAR and death receptor expression of prostate cancer cells

Oncolytic adenovirus and apoptosis inducer TRAIL are promising cancer therapies. Their antitumor efficacy, when used as single agents, is limited. Oncolytic adenoviruses have low infection activity, and cancer cells develop resistance to TRAIL-induced apoptosis. Here, we explored combining prostate-restricted replication competent adenovirus-mediated TRAIL (PRRA-TRAIL) with lovastatin, a commonly used cholesterol-lowering drug, as a potential therapy for advanced prostate cancer (PCa). Lovastatin significantly enhanced the efficacy of PRRA-TRAIL by promoting the in vivo tumor suppression, and the in vitro cell killing and apoptosis induction, via integration of multiple molecular mechanisms. Lovastatin enhanced PRRA replication and virus-delivered transgene expression by increasing the expression levels of CAR and integrins, which are critical for adenovirus 5 binding and internalization. Lovastatin enhanced TRAIL-induced apoptosis by increasing death receptor DR4 expression. These multiple effects of lovastatin on CAR, integrins and DR4 expression were closely associated with cholesterol-depletion in lipid rafts. These studies, for the first time, show correlations between cholesterol/lipid rafts, oncolytic adenovirus infection efficiency and the antitumor efficacy of TRAIL at the cellular level. This work enhances our understanding of the molecular mechanisms that support use of lovastatin, in combination with PRRA-TRAIL, as a candidate strategy to treat human refractory prostate cancer in the future.     

ErbB-2 signaling is involved in regulating PSA secretion in androgen-independent human prostate cancer LNCaP C-81 cells

The expression and secretion of prostate-specific antigen (PSA) are regulated by androgens in normal prostate secretory epithelial cells. In prostate cancer patients, the serum PSA level is usually elevated and cancer cells are initially responsive to androgens. However, those cancer cells become androgen-independent after androgen ablation therapy. In hormone-refractory cancer patients, even in an androgen-deprived environment, the circulation level of PSA rebounds and is constitutively elevated through a yet unknown mechanism. Tyrosine phosphorylation of ErbB-2 is involved in regulating the androgen-responsive phenotype of prostate cancer cells, and it is at least partly regulated by the cellular form of prostatic acid phosphatase (PAcP), a prostate-unique protein tyrosine phosphatase. We investigated the ErbB-2 signal pathway in androgen-independent PSA secretion. LNCaP C-81 cells, which are androgen-independent LNCaP cells lacking endogenous PAcP expression with a hypertyrosine phosphorylated ErbB-2, secreted a higher level of PSA in conditioned media than did androgen-sensitive LNCaP C-33 parental cells. A restored expression of cellular PAcP in C-81 cells was concurrent with a decrease in tyrophosphorylation of ErbB-2 and reduction of PSA secretion. Moreover, transient transfection of C-33 cells with the wild-type ErbB-2 or a constitutively active mutant of MEK1 cDNA resulted in an increased level of secreted PSA. The elevation of secreted PSA level by the forced expression of ErbB-2 was inhibited by an MEK inhibitor, PD98059. In C-81 cells, the expression of a dominant negative mutant of ErbB-2 reduced the secreted level of PSA. The inhibition of ErbB-2 or mitogen-activated protein (MAP) kinases by specific inhibitors AG879, AG825, or PD98059 led to a decrease in PSA secretion. Taken together, our data clearly indicate that the ErbB-2 signal pathway via MAP kinases (ERK1/2) is involved in regulating the secretion of PSA by androgen-independent human prostate cancer LNCaP C-81 cells in an androgen-depleted environment.     

Antibody to vascular endothelial growth factor slows growth of an androgen-independent xenograft model of prostate cancer.

PURPOSE: Human tumors are dependent on angiogenesis for growth, and vascular endothelial growth factor (VEGF) is a major regulator of this process. We aimed to study clinical utility of a recombinant humanized monoclonal anti-VEGF antibody (rhu alpha VEGF) in the treatment of the CWR22R androgen-independent xenograft model of prostate cancer. Experimental Design: rhu alpha VEGF has previously shown clinical activity in several xenograft cancer models. We administered 5 mg/kg rhu alpha VEGF i.p. twice weekly as a single agent and together with paclitaxel to established CWR22R xenografts. RESULTS: rhu alphaVEGF inhibited established tumor growth by 85% (P < 0.01 for trajectories of the average tumor volumes of the groups) at 3 weeks, but after cessation of rhu alpha VEGF treatment, tumor regrowth ensued. A paclitaxel dosage of 6.25 mg/kg s.c. five times/week slowed tumor growth (72% compared with controls at 3 weeks, P = 0.02). The combination of paclitaxel and rhu alpha VEGF resulted in greater inhibition of tumor growth than that observed with either agent alone (98% growth inhibition, P = 0.024 versus rhualpha VEGF alone and P = 0.02 versus paclitaxel alone). Paclitaxel alone had no antiangiogenic effects at the dosage studied, whereas rhu alpha VEGF had significant inhibition of angiogenesis, noted by microvessel density and CD34 staining. CONCLUSIONS: rhu alpha VEGF has cytostatic clinical activity in this androgen-independent prostate cancer xenograft model, and the addition of paclitaxel demonstrates increased clinical activity.     

Differential effects of PXD101 (belinostat) on androgen-dependent and androgen-independent prostate cancer models

Histone deacetylase inhibitors (HDACi) are promising epigenetic cancer chemotherapeutics rapidly approaching clinical use. In this study, we tested using in vitro and in vivo models the differential biological effects of a novel HDAC inhibitor [belinostat (PXD101)], in a wide panel of androgen-sensitive and androgen-independent tumor cells. Belinostat significantly increased acetylation of histones H3 and H4. Belinostat potently inhibited the growth of prostate cancer cell lines (IC50 range from 0.5 to 2.5 μM) with cytotoxic activity preferentially against tumor cells. This agent induced G2/M arrest and increased significantly the percentage of apoptosis mainly in androgen-sensitive tumor cells confirming its growth-inhibitory effects. The cell death mechanisms were studied in three different prostate cancer cell lines with different androgen dependence and expression of androgen receptor; LAPC-4 and 22rv1 (androgen-dependent and expressing androgen receptor) and PC3 (androgen-independent not expressing androgen receptor). Belinostat induced the expression of p21 and p27, acetylation of p53 and G2/M arrest associated with Bcl2 and Bcl-Xl downmodulation and significant reduction of survivin, IAPs and Akt/pAkt and increased caspase-8 and -9 expression/activity. Belinostat effectiveness was dependent on the androgen receptor (AR), since the stable transfection of AR greatly increased the efficacy of this HDAC inhibitor. These observations were correlated using in vivo models. We demonstrated that belinostat preferentially resulted in antitumor effect in androgen-dependent tumor cells expressing AR. Our findings provide evidence that belinostat may be a promising anticancer drug for prostate cancer expressing AR, supporting its clinical role in prostate cancer.     

Inhibition of transformed cell growth and induction of cellular differentiation by pyroxamide, an inhibitor of histone deacetylase.

PURPOSE: We have synthesized a series of hybrid polar compounds that induce differentiation and/or apoptosis of various transformed cells. These agents are also potent inhibitors of histone deacetylases (HDACs). Pyroxamide (suberoyl-3-aminopyridineamide hydroxamic acid) is a new member of this class of compounds that is currently under development as an anticancer agent. We investigated the activity of pyroxamide as an inducer of differentiation and/or apoptosis in transformed cells. EXPERIMENTAL DESIGN AND RESULTS: Pyroxamide, at micromolar concentrations, induced terminal differentiation in murine erythroleukemia (MEL) cells and caused growth inhibition by cell cycle arrest and/or apoptosis in MEL, prostate carcinoma, bladder carcinoma, and neuroblastoma cells. Administration of pyroxamide (100 or 200 mg/kg/day) to nude mice at doses that caused little evident toxicity significantly suppressed the growth of s.c. CWR22 prostate cancer xenografts. Despite the potent growth-inhibitory effects of pyroxamide in this tumor model, serum prostate-specific antigen levels in control versus pyroxamide-treated mice were not significantly different. Pyroxamide is a potent inhibitor of affinity-purified HDAC1 (ID(50) = 100 nM) and causes the accumulation of acetylated core histones in MEL cells cultured with the agent. Human CWR22 prostate tumor xenografts from mice treated with pyroxamide (100 or 200 mg/kg/day) showed increased levels of histone acetylation and increased expression of the cell cycle regulator p21/WAF1, compared with tumors from vehicle-treated control animals. CONCLUSIONS: The findings suggest that pyroxamide may be a useful agent for the treatment of malignancy and that induction of p21/WAF1 in transformed cells by pyroxamide may contribute to the antitumor effects of this agent.     

Selective induction of cell cycle arrest and apoptosis in human prostate cancer cells through adenoviral transfer of the melanoma differentiation-associated -7 (mda-7)/interleukin-24 (IL-24) gene

We have previously reported that overexpression of the melanoma differentiation-associated gene -7 (mda-7) using a replication-defective adenovirus (Ad-mda7), results in tumor-specific growth suppression and induction of apoptosis in wide variety of cancer cells. In the present study, we investigated the antitumor activity of Ad-mda7 and the underlying mechanism in human prostate cancer cells and normal prostate epithelial cells. Overexpression of MDA-7 induced significant (P=.001) suppression of cell growth and apoptosis in prostate cancer cells (DU 145, LNCaP, and PC-3). In normal prostate epithelial cells (PrEC) some degree of growth inhibition but not apoptosis was observed. However, the inhibitory effects in normal cells were less compared to tumor cells. Growth inhibitory effects were mediated by the intracellular and not by extracellular MDA-7 protein. Molecular effectors that are involved in Ad-mda7-mediated tumor killing included activation of the caspase cascade, and the induction of G2 phase cell cycle arrest through the inhibition of Cdc25C pathway. These results demonstrate the mechanisms by which Ad-mda7 exerts its antitumor activity in human prostate cancer cells. The antitumor activity combined with previously reported antiangiogenic and proimmune properties of Ad-mda7 can serve as a potential therapeutic agent for treatment of primary and disseminated prostate cancer.